Metal content and biochemical analyses of a recombinant collagenase PrtV from Vibrio parahaemolyticus

Quorum-Sensing Regulator OpaR Directly Represses Seven Protease Genes in Vibrio parahaemolyticus

Proteases play a key role in numerous bacterial physiological events. Microbial proteases are used in the pharmaceutical industry and in biomedical applications. The genus Vibrio comprises protease-producing bacteria. Proteases transform polypeptides into shorter chains for easier utilization. They also function as a virulence factor in pathogens. The mechanism by which protease genes are regulated in Vibrio parahaemolyticus, an emerging world-wide human pathogen, however, still remains unclear. Quorum sensing is the communication system of bacteria. OpaR is the master quorum-sensing regulator in V. parahaemolyticus. In the present study, quantitative reverse transcriptase-polymerase chain reaction and protease gene promoter-fusion reporter assays revealed that OpaR represses seven protease genes—three metalloprotease genes and four serine protease genes—which are involved in environmental survival and bacterial virulence. Furthermore, the electrophoresis mobility shift assay demonstrated that OpaR is bound directly to the promoter region of each of the seven protease genes. DNase I footprinting identified the sequence of these OpaR-binding sites. ChIP-seq analyses revealed 435 and 835 OpaR-binding sites in the late-log and stationary phases, respectively. These OpaR-binding sequences indicated a conserved OpaR-binding motif: TATTGATAAAATTATCAATA. These results advance our understanding of the protease regulation system in V. parahaemolyticus. This study is the first to reveal the OpaR motif within V. parahaemolyticus in vivo, using ChIP-seq, and to provide a database for OpaR direct regulon.

Proteases produced by vibrios

Bacteria of the genus Vibrio are normal habitants of the aquatic environment but the some species are believed to be human pathogens. Pathogenic vibrios produce various pathogenic factors, and the proteases are also recognized to play pathogenic roles in the infection: the direct roles by digesting many kinds of host proteins or indirect roles by processing other pathogenic protein factors. Especially VVP from Vibrio vulnificus is thought to be a major pathogenic factor of the vibrio. Although HA/P, the V. cholerae hemagglutinin/protease, is not a direct toxic factor of cholera vibrio, its significance is an undeniable fact. Production of HA/P is regulated together with major pathogenic factors such as CT (cholera toxin) or TCP (toxin co-regulated pilus) by a quorum-sensing system. HA/P is necessary for full expression of pathogenicity of the vibrio by supporting growth and translocation in the digestive tract. Processing of protein toxins such as CT or El Tor hemolysin is also an important pathogenic role.

The metalloprotease PrtV from Vibrio cholerae

The Vibrio metalloprotease PrtV was purified from the culture supernatant of a Vibrio cholerae derivative that is deficient in several other secreted peptidases, including the otherwise abundant hemagglutinin/protease HapA. The PrtV is synthesized as a 102 kDa protein, but undergoes several N- and C-terminal processing steps during V. cholerae envelope translocation and prolonged incubation. Purified V. cholerae PrtV protease forms of 81 or 73 kDa were stabilized by calcium ions. Removal of calcium resulted in further rapid autoproteolysis. The two major products of autoproteolysis of the PrtV protease were approximately 37 and 18 kDa and could not be separated under non-denaturing conditions, indicating they are interacting domains. In an assay using cultured cells of the human intestinal cell line HCT8, the PrtV protein showed a cytotoxic effect leading to cell death. Using human blood plasma as a source of potential substrates of mammalian origin for the PrtV protease, we found that the extracellular matrix components fibronectin and fibrinogen were degraded by the enzyme. Additional tests with individual protein substrates revealed that plasminogen was also a possible target for the PrtV protease.

Differential gene expression and extracellular secretion of the collagenolytic enzymes by the pathogen Vibrio parahaemolyticus

Vibrio parahaemolyticus, a causative agent of wound infections as well as food poisoning, harbors two collagenase genes: vppC and prtV. When cultivated at 26 degrees C in gelatin broth supplemented with 3.0% NaCl, significant collagenolytic activity was detected in the culture supernatant at the early stationary phase. Native polyacrylamide gel electrophoresis analysis revealed a 90-kDa protein, and N-terminal amino acid sequencing showed that this protein was VppC, generated through truncation of 72 N-terminal amino acid residues. Additionally, significant expression of only vppC was observed by reverse transcriptase PCR. By contrast, a vppC-negative mutant constructed through single crossover homologous recombination secreted a 50-kDa-collagenolytic enzyme; however, this enzyme was a serine protease that was reported previously. These results suggest that VppC is a primary extracellular collagenase produced by V. parahaemolyticus.

Expression and characterization of a metalloprotease from a Vibrio parahaemolyticus isolate

The extracellular zinc metalloprotease from Vibrio parahaemolyticus (VPM) is a putative virulence factor for host infection. It is synthesized from the vpm gene of V. parahaemolyticus as a polypeptide of 814 amino acids with an estimated molecular mass of 89,833 Da, containing a zinc metalloprotease HEXXH consensus motif. To investigate the enzymatic properties of V. parahaemolyticus metalloprotease, the mature vpm gene was overexpressed in Escherichia coli, and the recombinant protein (rVPM) was purified by a His-binding metal affinity column (>95% purity). The activity of the recombinant protease produced in E. coli was examined by gelatin activity staining and proteolytic activity assays using gelatin and azocasein as substrates. rVPM showed maximum activity at about 37 degrees C and pH 8. The cytotoxicity against flounder gill cells and fish pathogenicity indicated a potential role in pathogenesis.

Vibrio vulnificus and V. parahaemolyticus necrotising fasciitis in fishermen visiting an estuarine tropical northern Australian location

Three cases of severe necrotising fasciitis due to Vibrio vulnificus (two cases) and Vibrio parahaemolyticus (one case, fatal), have occurred in Caucasian tourists while fishing at a remote tropical northern Australian estuarine area. Infections were acquired over a 4-year period during the tourist fishing season (April to July 2000-2003), when water temperatures range from 23 to 30 degrees C. They are notable for their geographical clustering in the remote western aspect of the Gulf of Carpentaria, an area characterised by sedimentary stratiform zinc-lead-silver deposits and a major mining operation. Patients presented with classical bullous cellulitis with necrotising fasciitis, accompanied by severe sepsis. Underlying risk factors were identified in each patient; in one instance, previously unrecognised haemochromatosis was diagnosed. Likely reasons for Vibrio occurrence in this particular ecological niche are discussed.

Characterization of the enzyme activity of an extracellular metalloprotease (VMC) from Vibrio mimicus and its C-terminal deletions

To investigate the enzymatic properties of Vibrio mimicus metalloprotease, the mature metalloprotease gene (vmc) was overexpressed in Escherichia coli and the recombinant protein (rVMC61) was purified by metal affinity chromatography. rVMC61 showed maximum activity at about 37 degrees C, pH 8. The purified rVMC61 was very specific toward collagen substrates, such as gelatin, type I, II, and III collagens and synthetic peptides (Cbz-GPLGP and Cbz-GPGGPA). But it did not show degrading activity toward other biological proteins including lysozyme, lactoferrin and bovine serum albumin. rVMC61 also showed cytotoxicity against CHSE-214 fish cells. To examine the role of the C-terminal region of rVMC61, the 3' end of the metalloprotease gene (vmc) was digested serially with exonuclease III. The truncated vmc derivatives encoding 57-42 kDa of the protease were isolated and overexpressed in E. coli. The collagenase activities of truncated proteins were investigated using gelatin as substrate. Deletion of 100 amino acids from the C-terminus resulted in loss of gelatin degrading activity. However, deletion of 67 amino acids from the C-terminus did not affect its gelatin degrading activity.

Purification and characterization of a putative virulence factor, serine protease, from Vibrio parahaemolyticus

A protease (protease A) was successfully purified from the extracellular proteins of Vibrio parahaemolyticus no. 93, a clinical strain carrying neither tdh nor trh genes, using phenyl-Sepharose CL-4B hydrophobic interaction chromatography. The molecular mass of protease A was 43 kDa using gel filtration, which was in agreement with the results obtained from SDS-PAGE, suggesting that protease A was a monomeric protein. Additionally, the isoelectric point of this protein was 5.0. The optimum temperature and pH of protease A ranged from 40 degrees C to 50 degrees C and pH 8, respectively. Protease A activity was inhibited by serine protease inhibitors, such as phenylmethylsulfonyl fluoride and soybean trypsin inhibitor; moreover, the activity could be blocked by treatment with 20 mM of 1,10-phenanthroline, but could not be restored by adding metal ions. These results indicated that protease A is a serine protease that requires metal. The 12 N-terminal residues of protease A showed a high degree of identity (81%) to the sequence of Vibrio metschnikovii VapT serine protease. The purified protease had significant effects on the growth of Chinese hamster ovary, HeLa, Vero and Caco-2 cells and its cytotoxic activity was not blocked by gangliosides. Protease A lysed erythrocytes well but its hemolytic activity was unstable after heat treatment, indicating that protease A is able to cause hemolysis but is a heat-labile protein. The purified protease caused tissue hemorrhage and death in mice when injected both intraperitoneally and intravenously. In conclusion, this is the first report of a serine protease purified directly from the supernatant of V. parahaemolyticus and identifying it as a potential virulence factor.